Here you go, with explanation in comments.

import pandas as pd
from stockstats import StockDataFrame as Sdf

data   = pd.read_csv('data.csv')

stock  = Sdf.retype(data)

signal = stock['macds']        # Your signal line
macd   = stock['macd']         # The MACD that need to cross the signal line
#                                              to give you a Buy/Sell signal
listLongShort = ["No data"]    # Since you need at least two days in the for loop

for i in range(1, len(signal)):
    #                          # If the MACD crosses the signal line upward
    if macd[i] > signal[i] and macd[i - 1] <= signal[i - 1]:
        listLongShort.append("BUY")
    #                          # The other way around
    elif macd[i] < signal[i] and macd[i - 1] >= signal[i - 1]:
        listLongShort.append("SELL")
    #                          # Do nothing if not crossed
    else:
        listLongShort.append("HOLD")

stock['Advice'] = listLongShort

# The advice column means "Buy/Sell/Hold" at the end of this day or
#  at the beginning of the next day, since the market will be closed

print(stock['Advice'])